Chemical Changes

Chemical Change:

• process that produces new substance (s)
• Particles of substance are broken apart
• Atoms are rearranged into new particles, forming a new substance

Types of Chemical Changes/ Reaction:

• Combination -> 2 or more elements combine to form a new product compound involving energy change
• Combustion-> a substance burns in oxygen to produce new product (s)
• Thermal (heat) Decomposition-> A compound breaks down into 2 or more smaller substances
• Precipitation -> 2 aqueous solutions are mixed to form one solid product (precipitate)
• Photosynthesis
• Respiration

How to define if its  a chemical/ physical change

INFORMATION ON WORD EQUEATION:

http://www.mikecurtis.org.uk/reactions.htm

Burning 
This is when a substance reacts with oxygen and produces a flame.

Burning always produces an OXIDE.

Burning an element produces ONE oxide.

Burning a compound produces TWO or more oxides.

The mass of the oxides formed will always be MORE than the mass of the substance being burned. (why?)

eg i. Burning magnesium

Burns with bright white flame to form magnesium oxide

Word equation: Magnesium + oxygen ----> magnesium oxide

Burning Methane (natural gas)

Methane is a COMPOUND of carbon and hydrogen. (ie a hydrocarbon. other hydrocarbons are wax, petrol)

It burns with a smoky flame to form carbon dioxide and water

Word equation: Methane + oxygen ------> carbon dioxide and water

Alcohol will also burn to form carbon dioxide and water.

2. Decomposition

This is when a compound splits apart and forms two (or more) new substances.. (Each of the new substances contains atoms that was there to start with)

note : Elements can NEVER decompose because they are only contain ONE kind of atom.

Each new substance formed will have LESS mass than the original substance

eg i. Heating copper sulphate

Copper sulphate DECOMPOSES and forms water vapour, leaving white anhydrous copper sulphate.

Word equation: Hydrated copper sulphate ----> anhydrous copper sulphate + water

NOTE: This reaction is reversible. If water is added to anhydrous copper sulphate then the solution turns blue again accompanied by a rise in temperature.

Heating copper carbonate The copper carbonate DECOMPOSES forming carbon dioxide gas and leaving copper oxide. 

Word equation: Copper carbonate ----> copper oxide + carbon dioxide

iii. Heating limestone

The limestone decomposes and forms LIME and carbon dioxide gas

Word equation: Calcium carbonate -----> calcium oxide + carbon dioxide

or Limestone -----> lime + carbon dioxide

Reactions in Biology

 i Respiration 
Respiration is the reaction that takes place in ALL living organisms that releases energy from sugar. This energy is used by the organisms for essentials like growth, movement and warmth

Word equation: Glucose + oxygen ----> carbon dioxide + water

ii Photosynthesis
This is the reaction that takes place in the chloroplasts (found mainly in leaves) of plant cells

It converts carbon dioxide and water into sugar and starch, using energy from the sun.

Word equation    Carbon dioxide + water -----------> glucose + oxygen 
(Chlorophyll+ sunlight)

Precipitation 

e.g. lead (ll) nitrate + potassium iodide -> potassium nitrate + lead (II) iodide

Combination :

e.g. Potassium + chlorine gas -> Potassium chloride

JUST FOR LAUGHS :D

Physical Phenomena

Types of Physical Phenomena:

Heat gained: 

• Melting
• Boiling
• Evaporation
• Sublimation

Heat loss:

• Freezing
• Condensation
• Deposition

Others:

• Dissolving
• Diffusion

Physical Phenomena can be explained through Kinetic Particle Theory:

Example of heat gained ( Melting ):
Particles in solid only vibrate in fixed positions due to strong forces of attraction holding them closely together.
Upon heating, heat energy is absorbed by the particles of the liquid. The heat energy is converted into kinetic energy. The particles move faster as the temperature rises. When the temperature is high enough to reach melting point of water, the heat energy taken in is used to overcome the forces of attraction holding the particles together.
After melting is completed, heat energy is taken in to increase the kinetic of the particles, which now slides past each other continuously at a higher average speed.

Example of heat loss (Desublimation):
Particles in gas state move far apart from each other in a random direction and constant motion.
Upon cooling, heat energy is loss and the particles lose kinetic energy. The particles move slower as the temperature decreases. When the temperature os low enough to reach the desublimation point, the attractive forces of the particles strengthen as the particles does not have sufficient energy to overcome the forces.
After desublimation is completed, heat energy loss decreases the kinetic energy of the particles which vibrate in fixed positions in constant motion at a slower average speed due to strong attractive forces holding them close together.

Diffusion:
      Diffusion of a substance eg. a drop of ink in a glass of water; is evidence of matter being made up of tiny particles in constant random motion.
    When a drop of ink is added to a glass of water, it is observed that the ink spreads to different parts of the water without the need to stir.
   If particles are not already moving constantly, the ink would not be observed to spread on its own.
    There is no fixed pattern or direction to the movement/spread of the ink, indicating that the movement is random.

Assumptions and Limitations.

However, there are Limitations and Assumptions are made when using KPT model to explain the physical phenomena.

Assumptions:

(refer to handout given)

Limitations

(refer to handout given)